Unravelling depth layers of microbial communities, nitrogen transformation rate, and extracellular polymeric substances in anammox granules

Abstract

Anammox granules harbor a variety of bacteria, with each granule layer providing a niche for bacteria with specific metabolic functions. To investigate microbial distribution, nitrogen transformation rates, and extracellular polymeric substance (EPS) content across the depth layers of anammox granules, granules sized 0.9-2.0 mm were sheared into seven layers. The outer layers exhibited higher anammox bacterial abundance (9.9 %) than the inner layers (8.1 %). In contrast, the abundance of denitrifying bacteria increased from 25.0 % in outer layers to 34.9 % in inner layers. Nitrifying bacteria, along with heterotrophic nitrifying and aerobic denitrifying bacteria, were predominantly found in outer layers. Despite the higher EPS content in inner layers, denitrification rates remained low across all layers, likely due to limited carbon availability from microbial lysis or EPS. These findings offer valuable insights into the niche distribution of microbial communities within anammox granules.

Keywords: Anammox granule; Anammox rate; EPS; Microbial distribution.